(1) Field of the Invention
This invention relates to composite sucker rods for wells and more particularly to couplings for the sucker rod.
(2) Description of Related Art
Oil field wells are often over 20,000 feed deep. Sucker rods, which are usually manufactured in lengths of about 25', 30' or 37' are joined together by means of couplings to form a rod string which extends the length of the well casing. In a typical well, this rod string connects the "horse-head" to the piston in the pump at the base of the well. With each stroke of the piston, oil is forced up to the surface through the annulus between the rod and the tubing.
In recent years, composite rods have been used to form the individual sucker rods of the string. The composite rods exhibit many characteristics which make them superior to steel rods. In using composite rods the couplings to couple one length of sucker rod to the next have caused problems.
In this specification, the term "composite rod" should not be equal to glass fiber rods. In the technology today the composite rods consist typically of a high strength fiber other than glass which are bonded together into a single rod. Those having ordinary skill in the art will recognize that these fibers may be of carbon or aromatic polyarmide (commonly known by Du Pont's Trademark KEVLAR) or other substance. The term composite rods is used herein to indicate a manufactured material having high tensile strength.
Normally the couplings by nature will be larger in diameter than the rods which they connect together. However, it is desirable that they not be excessively large otherwise they will form an obstruction to the flow of fluid (oil) in the annulus between the rod and its coupling and the tubing. The limit to which the diameter of the coupling can be reduced is limited inasmuch as normally the strength of the coupling in tension is equal to or greater than the strength of the rod.
Also the joining of the composite material to the steel of the coupling has been a problem.
Traditionally and according to API specifications the sucker rods in oil wells will have a pin on each end of the rod. The rods will be connected together by a coupling unit which is typically less than 12 inches in length and has a box or female connection on each end thereof.
Prior connections included placing the rod directly within the socket, and holding it in place with epoxy. The stretching of the rod led to the breaking up and failure of the epoxy. Subsequently, there would be nothing to hold the rod in place. Its movements would then be erratic. Gluing the rod into the socket directly also made repairs more difficult on either of them.
Prior attempts to hold a composite rod within a tapered sleeve by the use of wedges has met with failure when the wedges were not adhered to the rod. I.e., to attempt to connect the rod within a socket as is shown with steel cable in CARLSON, (discussed below) have not been suitable for a composite rod.
Likewise, attempts to insert a composite rod into a socket with a tapered form in a socket and to pour epoxy or other resins or liquid composite material into the blind hole around the rod have not been satisfactory. The main problem has been the inability to form a good bond between the material forming the expansion cone and the rod itself.
FIG. 5 illustrates a unit commercially on the market which is most similar to this invention. Socket 38 has pin 40 upon one end. Tapered blind hole 42 is on the end opposite the pin. Composite rod 44 will be inserted within the blind hole and liquid resin poured in the blind hole 42 to form an expansion portion 46 around the rod 44 within the blind hole. The socket unit 38 as prepared in this way would be connected into a string by conventional box end couplers 48.
Before this application was filed, a search was made in the United States Patent and Trademark Office. That search developed the following United States Patents:
BUTLER et al. U.S. Pat. No. 991,196 PA1 SHAFFER et al. U.S. Pat. No. 1,384,489 PA1 HOWARD et al. U.S. Pat. No. 3,168,340 PA1 CARLSON et al. U.S. Pat. No. 4,205,926 PA1 SABLE et al. U.S. Pat. No. 4,249,831 PA1 PRIDY et al. U.S. Pat. No. 4,329,124 PA1 PETTERSON et al. U.S. Pat. No. 4,497,866
CARSLON discloses coupling sections of steel cable into a sucker rod string. Generally all of CARLSON'S disclosure follows the conventional teaching that a pin is placed on each end of each rod unit. However, in FIG. 18, CARLSON discloses a box coupling. CARLSON does not disclose how the box couplings would be connected together. One assumes that the rod would have a box on one end an pin on the other.
The metal on the pin end has minimum cross sectional area in the embodiments having pin connectors. I.e., the metal is removed to provide for the bore through the coupling leaving very little metal in the cross sectional area at the pin.
Also CARLSON chooses to use a shoulder between the tapered bore of his coupling and a cylindrical portion on his "inboard" or medial end. I.e., CARLSON'S tapered bore at the small end terminates with an inward facing shoulder. Therefore if through cylindrical stretch of the coupling (or for any other reason) the wedges of CARLSON butt against the shoulder it will cause a loosening of the grip of the wedges upon the cable. The only box connection CARLSON shows is in FIG. 18. At column 12, he states: "Generally speaking, the use of an internal wedging element in the strand permits lesser internal diameter passageway through the collar for a given size stand or cable than the use of external wedging elements as seen in FIGS. 18-20. The strand engaging means of FIGS. 1-3, inclusive gives greater gripping power than the devices of FIGS. 18-20, inclusive with no chance of strand turning on the collar." (Column 12, line 41-49)
The remaining patents are considered pertinent because the applicant believes the Examiner would consider anything revealed by the search to be relevant and pertinent to the examination of this application.